Note that layer-based resolution options will 'control' the map; you should typically only specify these things on the map or the layers, not both.

Note that the base layer controls the overall scales of the map; overlays will be entirely controlled by base layers.

Note that OpenLayers uses a DPI assumption of 72. To control this DPI setting, you can set OpenLayers.DOTS_PER_INCH before creating your map. A typical value (used by the SLD spec) will be different, so if this assumption matters to you, you should change this configuration parameter to match your server.